Keep in mind what The Template looks like in cross-section—a half circle that is twice as wide as it is tall. The slope assumes both sides taper as much as the top
The rear edge of the cab is basically a rectangle that is as wide as it is tall. Since there is twice as much taper in the sides, you wind up with a vertical trailing edge.
These are full bodies, instead of half-bodies; but include the squircle,
half-way between the square and the circle:
